1. Field of the Invention
This invention relates to cellular wireless communication systems, and more particularly, to a device and method for indicating whether user equipment carrier aggregation has been activated in a system for supporting carrier aggregation.
2. Description of the Related Art
Mobile communication systems have recently developed to achieve high data rate transmission via wireless channels, such as Orthogonal Frequency Division Multiple Access (OFDMA) or a Single Carrier Frequency Division Multiple Access (SC-FDMA). Multiple access is achieved by assigning or managing time-frequency resources that carry data or control information, to individual users, so that the resources cannot be superimposed, or by achieving orthogonality, thereby indentifying the data or control information respectively.
In order to provide high rate wireless data service in cellular wireless communication systems, one important factor is the ability to support scalable bandwidth. For example, Long Term Evolution (LTE) systems can support various bandwidths, such as 20, 15, 10, 5, 3, 1.4 MHz, etc. Service providers can select corresponding bandwidths to provide their services. There are various types of user equipment that can support bandwidths from 20 MHz to 1.4 MHz. LTE-Advanced (LTE-A) systems, intending to accommodate a service level of IMT-Advanced requirements, can provide a wide range of bandwidth, up to 100 MHz, via LTE carrier aggregation.
In order to achieve high rate data transmission, LTE-A systems require a wider range of bandwidth than LTE systems. Considering the backward compatability with LTE user equipment, LTE-A systems may also allow for the access of LTE user equipment and the usage of services. High rate data transmission can be achieved in LTE-A systems in such a way that: the entire system bandwidth is divided into component carriers (CC) or sub-bands of a bandwidth through which LTE user equipment can transmit or receive data; the component carriers are aggregated; data is created and transmitted, with respect to the respective component carriers; and transmission-reception processes of LTE systems are used with respect to the respective component carriers.
FIG. 1 illustrates an example of a configuration of an LTE-A system where the uplink and downlink each has three component carriers. For example, a reference of the aggregated component carriers is called an anchor carrier or anchor component carrier, and the others are called a non-anchor carrier or non-anchor component carrier. An eNode B or base station (BS) notifies user equipment (UE) of which one of the component carriers is set and managed as an anchor carrier, by performing an upper layer signaling operation. In general, it is assumed that the number of component carriers to be aggregated is set via an upper layer signaling operation. In downlink, a component carrier set as an anchor carrier may be a reference component carrier that transmits the initial system information, performs an upper layer signaling operation, and controls user equipment mobility. Likewise, in uplink, a component carrier, performing a random access operation after user equipment first accesses a system, may be an uplink anchor carrier.
As shown in FIG. 1, downlink and uplink are each operated via three aggregated component carriers, where a downlink component carrier, Downlink CC (DL CC) #0, and an uplink component carrier, Uplink CC (UL CC) #0, are set as anchor carriers of uplink and downlink, respectively. FIG. 1 shows an example of symmetrical carrier aggregation where the number of uplink component carriers is the same as the downlink component carriers; however, they can also be achieved with asymmetrical carrier aggregation where their numbers differ from each other.
As described above, LTE-A systems create and transmit data according to respective component carriers. Scheduling information regarding the transmitted data is Downlink Control Information (DCI) and reported to user equipment. DCI defines a variety of formats, and a format is determined according to whether it is scheduling information regarding uplink data or downlink data, whether it is compact DCI, whether spatial multiplexing using multiple antennas is applied, whether it is power controlling DCI, etc. For example, DCI format 1, regarding downlink data, without Multiple Input Multiple Output (MIMO), may include the following control information.                Resource allocation type 0/1 flag: report resource allocation type 0 or 1. Type 0 refers to a mode where resources are allocated, in units of resource block group (RBG), using bit-maps. The basic unit of scheduling in LTE and LET-A systems is resource block (RB) represented by time and frequency domains. An RBG includes a number of RBs and serves as the basic unit of scheduling in type 0. Type 1 refers to a mode where an RB is assigned in an RBG.        Resource block assignment: report RB allotted to data transmission. Resources, represented according to system bandwidth and resource allocation method, are determined.        Modulation and coding scheme: report coding rate and modulation used for data transmission.        HARQ process number: report HARQ process number.        New data indicator: report initial transmission or re-transmission of HARQ.        Redundancy version: report redundancy version of HARQ.        TPC command for Physical Uplink Control CHannel (PUCCH): report power control command for PUCCH as uplink control channel.        
The DCI is processed through channel coding and modulation, and then transmitted via Physical Downlink Control Channel (PDCCH) as a downlink physical control channel.
FIG. 2 illustrates an example where a base station schedules downlink data to user equipment in an LTE-A system where two carriers, DL CC #1 and DL CC #2, are aggregated. DCI 201 is transmitted via downlink component carrier #1 (DL CC #1) 209. DCI 201 is formatted, complying with the definition of LTE, channel-coded, and interleaved, thereby forming PDCCH 203. PDCCH 203 informs user equipment of scheduling information regarding Physical Downlink Shared Channel (PDSCH) 213 as a data channel allocated to user equipment, via DL CC#1 (209). DCI 205 is transmitted via downlink component carrier #2 (DL CC #2) 211. DCI 205 is formatted, complying with the definition of LTE, channel-coded, and interleaved, thereby forming PDCCH 207, PDCCH 207 informs user equipment of scheduling information regarding PDCCH 215 as a data channel allocated to user equipment, via DL CC#2 (211).
When user equipment is activated by the aggregation of N component carriers in LET-A system described above, if it does not receive the notification although real data is scheduled regarding only one component carrier, it must receive control channels with respect to respective component carriers in order to determine whether the N−1 component carriers are scheduled. This causes user equipment to consume electric power.